1. Field of the Invention
This disclosure relates in general to magnetic storage systems, and more particularly to a method and apparatus for providing a pole tip structure having a shape for preventing over saturation of the pole tip structure.
2. Description of Related Art
There has been huge progress in the field of magnetic storage system technology in almost 50 years. Moreover, the rate of this progress is increasing year after year. Such success has made storage systems an important component of modern computers.
Some of the most important customer attributes of any storage system are the cost per megabyte, data rate, and access time. In order to obtain the relatively low cost of today's storage system compared to solid state memory, the customer must accept the less desirable features of this technology, which include a relatively slow response, high power consumption, noise, and the poorer reliability attributes associated with any mechanical system. On the other hand, magnetic storage systems have always been nonvolatile; i.e., no power is required to preserve the data, an attribute which in semiconductor devices often requires compromises in processing complexity, power-supply requirements, writing data rate, or cost.
Improvements in areal density have been the chief driving force behind the historic improvement in storage cost. In fact, the areal density of magnetic storage systems continues to increase. While nature allows us to scale down the size of each bit of information, it does not allow scaling to happen forever.
Today, as the magnetic particles that make up recorded data on a storage system become ever smaller, technical difficulties in writing and reading such small bits occur. Further, as areal density increases, the requirements put on head designs will change.
In a magnetic head, a read element and a write element are formed having an air bearing surface ABS, in a plane, which can be aligned to face the surface of the magnetic disk. The read element includes a first shield, a second shield, and a read sensor that is located within a dielectric medium between the first shield and the second shield. The most common type of read sensor used in the read/write head is the magnetoresistive (AMR or GMR) sensor, which is used to detect magnetic field signal changes in a magnetic medium by means of changes in the resistance of the read sensor imparted from the changing magnitude and direction of the magnetic field being sensed.
The write element is typically an inductive write element that includes the second shield that functions as a first pole for the write element and a second pole disposed above the first pole. The first pole and the second pole contact one another at a backgap portion, with these three elements collectively forming the yoke. The combination of a first pole tip portion and a second pole tip portion near the ABS are sometimes referred to as the ABS end 56 of the write element. Some write elements have included a pedestal that can be used to help define trackwidth and throat height. A write gap is formed between the first and second poles in the area opposite the back gap portion. The write gap is typically filled with a non-magnetic, electrically insulating material that forms a write gap material layer. A conductive coil passes through the yoke. The write head operates by passing a writing current through the conductive coil. Because of the magnetic properties of the yoke, a magnetic flux is induced in the first and second poles by write currents passed through the coil. The write gap allows the magnetic flux to fringe out from the yoke thus forming a fringing gap field and to cross the magnetic recording medium that is placed near the ABS.
A critical parameter of a magnetic write element is the trackwidth of the write element, which defines track density. For example, a narrower trackwidth can result in a higher magnetic recording density. The trackwidth is defined by the geometries in the ABS end of the yoke. For example, the trackwidth can be defied by the width of the pedestal or by the width of the second pole. Alternatively, in designs that have no pedestal at all it would be possible to define the trackwidth by the width of the first pole.
One of the factors that influence the performance of the recording head includes a throat height (TH). The throat height refers to a length (height) of a magnetic pole between an air bearing surface and an edge of an insulating layer for electrically isolating thin film coils for generating a magnetic flux. The air bearing surface refers to a surface of the thin film magnetic head facing a magnetic recording medium and is sometimes called a track surface. A reduction in the throat height is desired for the improvement in the performance of the recording head because the length of the bit cell is largely dictated by a length of the write gap or throat height. Moreover, to further improve the areal density at which information can be recorded and reliably read. This desire has lead to a trend toward shorter bit length along a magnetic recording track and a shrinking trackwidth. As mentioned above, narrow trackwidths are achieved by use of narrow pole tips at an air bearing surface (ABS) of the head.
A top pole is typically formed over the throat insulator. The use of two-piece pole structures facilitates the achievement of a submicron pole tip width at the ABS. A two-piece pole structure employs a first piece (pole tip or cap layer) having a very narrow width at the ABS, and a second pole piece connected to the first pole piece and extending to the back region of the head. Thus, the first pole piece defines the narrow trackwidth, and the second pole piece links through the coils. One issue with the cap layer is that it may be over saturated and lose the ability to focus the flux to the center of a track. This would degrade the on-track writability and the unfocused flux may also cause adjacent track interference.
It can be seen then that there is a need for a method and apparatus for providing a pole tip structure having a shape for preventing over saturation of the pole tip structure.